TVA Looks at New "Worst Case" Flooding Scenario

AP

CHATTANOOGA (AP) – The Tennessee Valley Authority is developing a worst-case flooding scenario that could require taller dams and more protection for nuclear reactors.

According to the Chattanooga Times Free Press, utility officials were meeting Monday with the U.S. Nuclear Regulatory Commission in Atlanta to discuss nuclear plant safety from flooding.

Floods have not overtopped TVA's dams on the Tennessee River and its tributaries, but severe flooding on the Cumberland River caused problems in 2010 at U.S. Army Corps of Engineers dams above and below Nashville.

TVA began a series of temporary fixes three years ago.

The agency has since reassessed potential flooding and concluded a "probable maximum flood" will require building concrete walls and raising earth berms from 2.3 feet to 6.6 feet, depending on location.

Mike Eiffe, TVA program manager for hydrology and hydraulics, said that level of preparation means raising the levels of the dams and the earthen berms that flank them.

"The drainage area for Chattanooga is a little over 20,000 square miles, and for the type of flood events that we're talking about, we would be looking at an average of 15 to 16 inches of rainfall over that entire 20,000-square-mile drainage area," he said.

Government experts define probable maximum flood as that which could be expected from the most severe combination of rain and river flow.

A September draft safety modification document notes that a public suggestion to "floodproof" the Watts Bar, Sequoyah and Browns Ferry nuclear plants with their own walls or levies would cost as much as $1 billion.

The utility says shutting down a nuclear reactor would cause $1 million per day in lost production.

TVA earlier placed sand baskets to raise the flanks of four dams by 3 to 8 feet after questions arose during talk of renewing construction at Bellefonte Nuclear Plant.

"I'm not so worried about the nuclear plants. But I think a flood like that would be a substantial threat to Chattanooga," said Hamilton County Emergency Management chief Bill Tittle.

"The weather systems are changing. We see and hear about it every day. If the Nashville rains had been a little east, that would have been us," Tittle said.